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Primer: pyramid and sqlalchemy are now formatted with latest Black (#1736)
[etc/vim.git] / fuzz.py
1 """Property-based tests for Black.
2
3 By Zac Hatfield-Dodds, based on my Hypothesmith tool for source code
4 generation.  You can run this file with `python`, `pytest`, or (soon)
5 a coverage-guided fuzzer I'm working on.
6 """
7
8 import hypothesmith
9 from hypothesis import HealthCheck, given, settings, strategies as st
10
11 import black
12
13
14 # This test uses the Hypothesis and Hypothesmith libraries to generate random
15 # syntatically-valid Python source code and run Black in odd modes.
16 @settings(
17     max_examples=1000,  # roughly 1k tests/minute, or half that under coverage
18     derandomize=True,  # deterministic mode to avoid CI flakiness
19     deadline=None,  # ignore Hypothesis' health checks; we already know that
20     suppress_health_check=HealthCheck.all(),  # this is slow and filter-heavy.
21 )
22 @given(
23     # Note that while Hypothesmith might generate code unlike that written by
24     # humans, it's a general test that should pass for any *valid* source code.
25     # (so e.g. running it against code scraped of the internet might also help)
26     src_contents=hypothesmith.from_grammar() | hypothesmith.from_node(),
27     # Using randomly-varied modes helps us to exercise less common code paths.
28     mode=st.builds(
29         black.FileMode,
30         line_length=st.just(88) | st.integers(0, 200),
31         string_normalization=st.booleans(),
32         is_pyi=st.booleans(),
33     ),
34 )
35 def test_idempotent_any_syntatically_valid_python(
36     src_contents: str, mode: black.FileMode
37 ) -> None:
38     # Before starting, let's confirm that the input string is valid Python:
39     compile(src_contents, "<string>", "exec")  # else the bug is in hypothesmith
40
41     # Then format the code...
42     try:
43         dst_contents = black.format_str(src_contents, mode=mode)
44     except black.InvalidInput:
45         # This is a bug - if it's valid Python code, as above, Black should be
46         # able to cope with it.  See issues #970, #1012, #1358, and #1557.
47         # TODO: remove this try-except block when issues are resolved.
48         return
49
50     # And check that we got equivalent and stable output.
51     black.assert_equivalent(src_contents, dst_contents)
52     black.assert_stable(src_contents, dst_contents, mode=mode)
53
54     # Future test: check that pure-python and mypyc versions of black
55     # give identical output for identical input?
56
57
58 if __name__ == "__main__":
59     test_idempotent_any_syntatically_valid_python()